The superoxide radical is a common intermediate in the biological reduction of oxygen. This radical constitutes a threat to the integrity of the cell. An enzymatic defense exists. This enzyme is called superoxide dismutase and it acts by catalyzing the following reaction: O minus over 2 plus O minus over 2 plus 2H plus yields H2O2 plus O2. Superoxide dismutases have already been isolated from a number of sources. We plan to continue our studies of the structure, mechanism and biological functions of these enzymes. Specifically, we plan to do the following: a. Isolate and characterize the SOD found in a red algae, a blue-green algae, an insect and the chloroplasts of higher plants. b. Continue collaborations with Drs. D. Richardson and R.L. Hill aimed at elucidating the complete structure of the bovine SOD. c. Isolate mutants of E. coli deficient in one or both of the SOD's found in this organism and correlate the enzymatic defects with their functional sequellae. d. Investigate the role of O minus over 2 and of SOD in oxygen toxicity, oxygen-enhancement of radiation damage and senescence. e. Investigate the role of O minus over 2 in oxidative hemolysis. f. Investigate the role of O minus over 2 in the phagocytic kill of bacteria by leukocytes.